Carbon dioxide generated by burning fossil fuels and other human activities is a big problem, when it comes to climate change. But researchers say that it actually may be possible not only to capture and store CO2 in the ground, but to transform it into the equivalent of a battery that would store energy from renewable sources and solve the supply fluctuations that hinder them as a replacement for coal.
A international group of scientists, which includes Lawrence Livermore National Laboratory researcher Tom Buscheck, recently proposed a design for such a carbon battery in a paper presented at the European Geosciences Union general assembly in Vienna. The idea is to store energy generated by renewable sources such as wind and solar power when electrical demand is low, and then tap into it at peak times. (The system could also store energy generated by burning coal as well.)
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That ability to store renewable energy would solve two problems at once, researchers explained in a New Scientist article. It would help create an economic incentive for carbon capture and sequestration, which they said has been slow to develop because it doesn't make money for power companies.
Second, the storage would make renewable energy available even at times when the wind dies down or the sun is behind clouds.
The process takes C02 that's been put in supercritical form - that is, a fluid state where it has both gaseous and liquid properties - and injects it into brine, or salty water, in rocks about a half-mile to 3 miles under the surface. Some of the brine is displaced toward the surface, where it can be heated with the surplus electricity and then circulated back down into the rocks to store the heat.
Back inside the Earth, the heated brine makes the carbon dioxide expand. The C02 can then be used to spin special turbines, which are 50 percent more efficient than ones driven by conventional steam.
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Buscheck said such a system could store 8 million tons of carbon dioxide each year for 30 years - about the same amount that a coal-burning power plant generates.
In 2013, Buscheck and colleagues also developed a system that would utilize sequestered C02 to help draw in underground heat to boost geothermal power generation.